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CCIE Network engineer Detailed router routing table

CCIE Network engineer must know

Detailed router routing table

The Internet connects various types of computers and other terminal devices in the world, so that these devices can work together and communicate with each other. In an IP network, the data follows the format defined by the IP protocol, and the device processes it accordingly so that it can be transmitted on the network.

CCIE Network engineer must know

In order to achieve this function, the devices in the network need to have the ability to forward IP packets from the source to the destination. When a router receives a packet, it queries the routing in its routing table to find the routing entry that matches the destination IP address of the packet. If a matching routing entry is found, the router will follow the entry The indicated outbound interface and next hop IP address forward the packet; if no route entry matches the destination IP address, it means that the router has no relevant routing information to guide the packet forwarding, so the packet will be discarded . This is how routers process data packets.

Every device with routing function will maintain a routing table. According to this routing table, the router can correctly forward IP packets. It is like a map. The routing table contains routing entries learned by the router through various channels. Each routing entry contains information such as the destination network address/net mask, routing protocol, outgoing interface, next-hop IP address, routing priority, and metric value.

The meaning of each message in the routing table is as follows:

1. Target IP address and netmask: As a map in a network, each route in it points to a destination network in the network. The network address and netmask of the destination network are used to identify a route.

2. Routing protocol: indicates the protocol type of the route or the way the route was learned. For example, OSPF, EIGRP, Static, etc., if it is a direct route, it will display “C”.

3. Priority: It can also be called the administrative distance. There are multiple sources for obtaining routing entries in the routing table. Each type of route corresponds to a different priority. The smaller the value of the route priority, the higher the priority of the route. high.

CCIE Network engineer must know

4. Metric value: refers to the substitute value of the router to the destination network segment. In many cases, it is also called metric value or metric value. The size of the metric value will affect the choice of routing. The smaller the metric value, the higher the path priority, and different routing protocols have different definitions and calculations for routing metric values.

5. Next-hop address: The next-hop address used by the router to forward packets arriving at the destination network segment. Simply put, it is equivalent to walking at a crossroads. The navigation (routing table) will tell us whether we should turn left or go straight.

6. Outgoing interface: the interface when the data packet leaves the router after being routed. When we receive a data packet, the router performs table lookup and forwarding, and the interface that forwards the data out of the router is the outgoing interface.

Any device that supports routing functions must maintain a routing table to correctly forward data. In a network, a router’s routing table often contains multiple routes, which may be obtained from different sources. Such as dynamic protocols or static routing.

CCIE Network engineer must know

The router can automatically obtain the route of the direct connection port of the device and write the route into the routing table. This route is called a direct connection route. The destination network of the direct connection route must be the network where a certain interface of the router itself is located. When the router interface status In the dual-UP state, direct routes appear in the routing table.

For routes to non-directly connected networks, routers must be obtained through other means. Static routing is the most direct and simplest method. Static routing is the route added by the administrator to the router using manual configuration. The network administrator uses manual configuration to tell the router what to do next. The configuration of static routes does not require network resources, and does not require interactive protocol packets.

There is also a default route. The default route is also called the default route. It is a route with a destination network address and a netmask of 0, that is, or This is a very special route, and all destination IP addresses can be matched by this route. Moreover, the default route can not only be implemented in a static way, but the dynamic routing protocol also supports the dynamic delivery of the default route.

The last one is the dynamic routing protocol. When in a large or medium-sized network, due to the large number of network segments and the complicated network topology, the configuration and maintenance workload of using static routing is too large, then you need to consider the dynamic routing protocol. .

When we start the dynamic routing protocol, routers can exchange routing information and automatically generate routing entries. When the network topology changes, the dynamic routing protocol can sense these changes and automatically respond, so that the routing information in the network adapts to the new topology. These things can be done by the router independently, without administrator intervention.

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